Significant Accounting Policies - Narrative (Detail) (USD $)	3 Months Ended
Mar. 31, 2015 Segment	Mar. 31, 2014	Dec. 31, 2014
Business Organization And Significant Accounting Policies [Line Items]
Number of business segment	1us-gaap_NumberOfOperatingSegments
Allowance for doubtful accounts	$ 0		$ 0
Transfers between fair value levels	0		0
Client Performance Period	5 years
Advance commissions amortization period	12 months
Contractual Expense Reimburse, Net	547,755dhil_ContractualExpenseReimburseNet	398,248dhil_ContractualExpenseReimburseNet
Liability for Uncertain Tax Positions, Current	0		0
Class A, C, and I Shares
Business Organization And Significant Accounting Policies [Line Items]
Rate of Administrative Service Fees	0.24%		0.25%
Class Y
Business Organization And Significant Accounting Policies [Line Items]
Rate of Administrative Service Fees	0.10%		0.10%
Mutual Funds \| Money Market Funds \| Level 1 Inputs
Business Organization And Significant Accounting Policies [Line Items]
Cash Equivalent Fair Value	26,600,000		31,800,000
Incentive Fees Method One [Member]
Business Organization And Significant Accounting Policies [Line Items]
Performance Incentive Fees	$ 0	$ 0

Advance commissions amortization period.

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- Definition

Cash equivalent fair value.

+ References

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- Definition

Contractual Expense Reimbursement netted against applicable expenses under agreement

+ References

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- Definition

Fair Value, Transfers Between Level 1, Level 2, or Level 3, Amount

+ References

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- Definition

Rate of administrative service fees.

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- Definition

Rolling Client Investment Performance Period

+ References

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- Definition

For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 4

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.4)

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The current portion of the amount recognized for uncertain tax positions as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.20)

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- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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- Definition

Amount of revenue earned by the entity based on the investment results achieved. Excludes fees based upon a percentage of the assets under management not performance-related.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.13 (a))

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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